Table 2.

Hazard ratios (HRs) and 95% confidence intervals (CIs) for thyroid cancer according to reproductive and hormonal factors.

	All Thyroid		Papillary Carcinoma
	Cases	HR (95% CI)a	Cases	HR (95% CI)a
Age at menarche
<12 years	33	1.00 (reference)	25	1.00 (reference)
12–13 years	70	0.84 (0.55–1.27)	57	0.91 (0.57–1.46)
≥14 years	24	0.62 (0.36–1.05)	17	0.60 (0.32–1.11)
P-trendb		0.08		0.11
Type of menopause
Natural	74	1.00 (reference)	58	1.00 (reference)
Hysterectomy, both ovaries removed	17	1.21 (0.71–2.06)	16	1.47 (0.84–2.56)
Hysterectomy, still has ≥1 ovaries/unknown	31	1.22 (0.80–1.86)	22	1.13 (0.69–1.85)
Age at natural menopausec,e
<50 years	21	1.00 (reference)	14	1.00 (reference)
50–54 years	34	1.08 (0.62–1.86)	29	1.38 (0.73–2.61)
≥55 years	19	2.24 (1.20–4.18)	15	2.65 (1.28–5.51)
P-trendb		0.02		0.01
Number of reproductive yearsd,e
<35 years	20	1.00 (reference)	14	1.00 (reference)
35–40 years	27	0.83 (0.46–1.48)	22	0.96 (0.49–1.88)
>40 years	27	1.71 (0.96–3.07)	22	1.97 (1.00–3.87)
P-trendb		0.05		0.03
Lifetime number of ovulatory cyclese
<415 cycles	22	1.00 (reference)	16	1.00 (reference)
415–489 cycles	28	1.27 (0.73–2.23)	25	1.54 (0.82–2.90)
≥ 490 cycles	24	2.40 (1.33–4.30)	17	2.27 (1.13–4.53)
P-trendb		0.01		0.02
Number of live births
Nulliparous	13	1.40 (0.69–2.85)	9	1.06 (0.44–2.60)
1 or 2	34	1.00 (reference)	26	1.00 (reference)
3	27	0.98 (0.59–1.63)	22	1.06 (0.60–1.87)
4	19	1.04 (0.59–1.83)	13	0.94 (0.48–1.85)
≥5	34	1.72 (1.05–2.82)	29	1.98 (1.14–3.43)
P-trendb,f		0.04		0.03
Age at birth of first child among parous womend
<20 years	26	1.00 (reference)	19	1.00 (reference)
20–24 years	60	0.83 (0.51–1.34)	47	0.89 (0.51–1.56)
≥25	27	0.60 (0.34–1.08)	23	0.68 (0.35–1.33)
P-trendb		0.09		0.26
Tried becoming pregnant without success
Never	107	1.00 (reference)	84	1.00 (reference)
Ever	20	1.10 (0.68–1.77)	15	1.05 (0.60–1.82)
Oral contraceptive use
Never	51	1.00 (reference)	42	1.00 (reference)
Ever	76	1.15 (0.79–1.68)	57	1.05 (0.69–1.60)
Hormone therapy status
Never	41	1.00 (reference)	33	1.00 (reference)
Former	18	0.86 (0.50–1.50)	14	0.83 (0.45–1.56)
Current	68	0.99 (0.67–1.49)	52	0.94 (0.60–1.48)
Tubal Ligation
Never	89	1.00 (reference)	70	1.00 (reference)
Ever	38	1.46 (0.99–2.16)	29	1.42 (0.91–2.23)

^aAdjusted for education (less than high school graduate, high school graduate, college graduate), race (non-Hispanic white, non-Hispanic black, Hispanic, Asian/Pacific Islander/American Indian), marital status (married or living as married, widowed, divorced/separated, never married), family history of thyroid cancer, baseline BMI status (<25 kg/m², 25–29 kg/m², ≥30 kg/m²), and smoking status (never smoked, former smoker, current smoker) with attained age as the underlying time variable

^bP-trend calculated by modeling the categorical variable as continuous

^cAge at natural menopause defined as when the participant reported having their last period

^dNumber of years between age at menarche and age at natural menopause

^eRestricted to women with natural menopause

^fExcludes participants reporting never pregnant or no live births